The present application relates to a light source using a master oscillator power amplifier (MOPA) in which a mode-lock oscillating laser is combined with an optical amplifier, and a recording apparatus using the light source.
A laser beam having high-peak power, particularly, intense pulsed light is very effective in implementing a non-linear multi-photon absorption process, and expected to be applied to three-dimensional optical recording or a ultrafine process using the absorption process, non-destructive bio-imaging, or the like.
For example, in “Seiji Kobayashi, Kimihiro Saito, Takashi Iwamura, Hisayuki Yamatsu, Toshihiro Horigome, Mitsuaki Oyamada, Kunihiko Hayashi, Daisuke Ueda, Norihiro Tanabe, and Hirotaka Miyamoto, ISOM2009 Digest Th-1-01, 2009,” a method of irradiating a transparent bulk material having a non-linear effect with a high-power laser beam and implementing multi-layer recording has been reported. This method represents a possibility of a recording medium which is cheaper and larger in capacity than a stack-type disk of a related art. A mode-lock type titanium-sapphire laser is used as a light source that emits a high-power laser beam. In the example of “Seiji Kobayashi, Kimihiro Saito, Takashi Iwamura, Hisayuki Yamatsu, Toshihiro Horigome, Mitsuaki Oyamada, Kunihiko Hayashi, Daisuke Ueda, Norihiro Tanabe, and Hirotaka Miyamoto, ISOM2009 Digest Th-1-01, 2009,” a light source for short wavelength recording advantageous for high-density recording is implemented such that emitting light with a wavelength of 810 nm emitted from the titanium-sapphire laser is converted into light with a wavelength of 405 nm by a second harmonic generator (SHG). The solid-state laser is large in device size and high in price, and thus its application is limited to experiments in laboratories (for example, see Spectra-Physics, [online], [searched on Aug. 6, 2010], Internet <URL:http://www.spectraphysics.jp/member/admin/document_upload/Tsunami_Series_Data_Sheet.pdf>).
In this regard, many researchers have made an attempt to develop a pulse light source which is smaller and cheaper in practical use based on a semiconductor. In next-general optical recording as in the above-mentioned method, a violet-blue laser source advantages to high-density recording is in strong demand.
For example, in a gain switching type laser, there have been reports that when oscillation of a laser beam is performed at a repetition frequency of 1 MHz by strong excitation driving, peak power of 55 W can be implemented (see M. Kuramoto, T. Oki, T. Sugahara, S. Kono, M. Ikeda, and H. Yokoyama, Appl. Phys. Lett. 96, 051102—2010_.). However, due to the demand on a high data transfer rate in the market, a high repetition frequency is necessary even in a light source for data recording.
In recent years, in a blue laser effective for high-density recording, there have been reported a light source in which a laser beam having peak power of 100 W oscillates at a repetition frequency of 1 GHz (for example, see Rintaro Koda, Tomoyuki Oki, Takao Miyajima, Hideki Watanabe, Masaru Kuramoto, Masao Ikeda, and Hiroyuki Yokoyama, APPLIED PHYSICS LETTERS 97, 021101—2010_). This light source is called an MOPA, and configured such that a semiconductor mode-lock laser is combined with a semiconductor optical amplifier.